#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[100];
    int i, len, lastwordlen = 0;
    fgets(s, sizeof(s), stydin);
    s[strcspn(s,"\n")] = '\0;
    len = strlen(s);
    for(i=0; i < len ; i++) {
        if(!(isalpha(s[i]) ||
        isspace(s[i]))) {
            printf("invalid input\n");
            return 0;
        }
    }
    i = len - 1;
    while(i >= 0 && isalpha(s[i])) {
        lastworldlen++;
        i--;
        if(lastworldlen > 0)
        printf(%d\n", lastworld len);
        else
        printf("invalid input\n");
        return 0;
    }